1. Field of the Invention
The present invention relates to a thin-film magnetic head for perpendicular magnetic recording.
2. Description of the Related Art
As is well known, a thin-film magnetic head for perpendicular magnetic recording includes an auxiliary magnetic pole layer, a main magnetic pole layer (single magnetic pole), and a nonmagnetic insulating layer disposed therebetween at a surface facing a recording medium. The area of the main magnetic pole layer exposed on the surface facing the recording medium is sufficiently smaller than that of the auxiliary magnetic pole layer. The auxiliary magnetic pole layer and the main magnetic pole layer are magnetically coupled to each other at a section behind the surface facing the recording medium. A coil layer of which the center is located at the magnetically coupled section is embedded in the nonmagnetic insulating layer. Upon energizing of the coil layer, a recording magnetic field is induced between the auxiliary magnetic pole layer and the main magnetic pole layer. Then a leakage recording magnetic field between ends facing the recording medium of these magnetic pole layers permeates through a hard film perpendicularly and passes through a soft film of the recording medium and then back to the ends. Since the leakage recording magnetic field is concentrated on a small area of the end of the single magnetic pole, magnetic data is recorded in a portion facing the end of the main magnetic pole layer.
Accordingly, the smaller the area of the single magnetic pole viewed from an end face facing the recording medium is, the higher the recording density is. In general, the thin-film magnetic head for perpendicular magnetic recording is provided on a trailing edge of a head assembly, and mounted on a slider. The head assembly has a center of oscillation at the exterior of a recording medium that rotates. Accordingly, if the shape of the single magnetic pole viewed from the end facing the recording medium is a rectangle, fringing, caused by an oblique leakage magnetic field due to the difference in the oblique direction between an inner circumference and an outer circumference of the recording medium corresponding to the corners of the rectangle, is generated. The fringing causes a reduction in signal to noise ratio S/N during the recording and a servo error. Accordingly, the shape of the main magnetic pole layer viewed from the end facing the recording medium is a substantially trapezoidal shape converging toward the auxiliary magnetic pole layer. Unfortunately, an ideal substantially trapezoidal shape of the main magnetic pole layer is difficult to achieve in the conventional structure.